Abstract

The thermodynamic properties of micellization
for dodecylphosphocholine (DPC), sodium dodecyl sulfate
(SDS), and their mixtures were studied using isothermal
titration calorimetry. NMR relaxation measurements were
used to explore molecular mobility of the DPC-containing
micelles, whereas the diffusion measurements were taken
to determine the micelle size. The DPC/SDS mixed sys-
tems reveal a tendency to form two kinds of micelles in
buffered solution at lower temperatures. An increase in
temperature as well as the transfer of the DPC/SDS mixed
micelles from buffered to unbuffered solution results in
only a single-step micellization process. The average size
of the DPC-containing micelles is only slightly dependent
on the SDS fraction. Examination of the data of spin–spin
relaxation (
T
2
) shows that methylene protons on the polar
headgroup of DPC and methylene protons (H1) on the
hydrocarbon chain in the micellar systems studied reveal a
heterogeneous dynamic behavior reflected in a two-
component
T
2
relaxation in the whole temperature range.
The latter is the main constituent of the rigid interfacial
layer core protecting the penetration of water into the
hydrophobic interior.